Juvenile Killer is the fifth stage in Squishy Cave.
Many Master A. will stack up. They just literally smash all your units in a second.
Lineup: Wall Cat, Macho Cat, Sexy Legs Cat, Dragon Cat, Bahamut Cat, and any other ranged cats (Paris cat, Skirt cat, etc.)
Begin by sending out 1-3 wall cats, to save up cash. When the first Master A. comes out, begin spamming Wall Cat and Macho Cat. These should be able to hold Master A. at a standstill. Now begin spamming all ranged units, and send out Bahaumut cat. Continue this, firing the cat cannon as soon as it loads. This should beat the level. Uber long range cats such as any of the nekolugas or Hacker cat are also incredibly helpful. If needed, bring a third meat shield such as Boogie cat.
Strategy 2 (The crush everything strategy)
If you have any uber rares that deal enough damage to one-shot Master A, then this level should be easy.
I'm going to use Sodom, as I beat this stage using him with this strategy. If you have an uber with massive damage and very high health (slow movement also helps), then that should work too.
Just drop meatshields, and save up for Sodom, and dropping Dragon Cats and Sexy Legs Cat.
Sodom will demolish the Master As, while the others will kill the peons
(Note: you may need Legendary Cat Sword at high level for all chapters. You should by now, but if you don't and want this stately to work, you need it.)
Strategy 3 (Late-game Strategy)
This strategy only works if you are returning to this stage late-game on higher star ratings. Use Awakened Bahamut to deal gargantuan damage to the Master A.s before dying, and use Li'l Nyandam for constant support. This becomes even more difficult on Four Star, as you cannot use meatshields or Uber Rares like Aphrodite. In that case, fire the Cat Cannon before Awakened Bahamut reaches the Master A.s, similar to what you would do on Oncoming Storm, so he can get a hit in without dying. Eventually, the Master A.s will be pushed behind the base, and you can complete the level.